Ammonia sensors may be used in exhaust emission control to maintain accurate control of injected reductant, such as injected urea. However, the inventors herein have recognized that depending on the ambient humidity, the ammonia reading from the sensor may be erroneous.
However, the inventors herein have also recognized that the errors due to ambient humidity manifest themselves in a predictable way across different air-fuel ratios. Further, the inventor have developed various approaches that correlate the sensor readings under selected conditions to ambient humidity. As such, the sensitivity to ambient humidity may be used to advantage, rather than viewed as purely a detrimental effect.
In one example, a method for an engine having an exhaust with an ammonia sensor includes adjusting an operating parameter in response to ambient humidity, the ambient humidity based on a first reading of the ammonia sensor at a first exhaust air-fuel-ratio and a second reading of the ammonia sensor at a second exhaust air-fuel-ratio.
In another example, a method using an ammonia sensor in an engine exhaust SCR system, includes in a first mode, identifying ambient humidity by measuring an ammonia concentration via the ammonia sensor during two different air-fuel-ratios, the measuring in response to an indication of a potential humidity change and may further include in a second mode, controlling an ammonia or urea injection dosage via feedback from the ammonia sensor, where during the first mode, ammonia or urea injection dosage is independent of current ammonia sensor feedback and based on previous ammonia sensor feedback. In still another example, a method for an engine having an ammonia sensor in an exhaust downstream of an SCR catalyst, includes during a first mode, adjusting ammonia injection in response to the sensor, and during a second mode, adjusting ammonia injection independent of the sensor while indicating ambient humidity based on the sensor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.